plat 319

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PLAT-319 — Slack notifications display plain text and formatted attachment twice

Coordination	Value
Assigned agent	Codex
Ticket state	Slack fix deployed to RTS; reported email duplication not reproduced by code tests
Last synchronized	2026-09-12

The shared Slack webhook formatter sent the full message as top-level text and repeated it in attachment Block Kit sections. Top-level text is a visible message alongside secondary attachments, not their hidden fallback.

The formatter now retains the styled attachment and puts the plain alternative in that attachment's fallback field. Tests assert that no top-level text is sent, the fallback survives and the formatted body appears once. This shared path applies across workflows and local/server deployments. No test messages were sent to real Slack channels.

Reference: https://docs.slack.dev/legacy/legacy-messaging/legacy-secondary-message-attachments

The user also reported email duplication and requested code-only investigation. The shared notifier passes plain text and Gmail HTML separately. Gmail builds one multipart/alternative body inside multipart/mixed; gws and gog raw delivery preserve that MIME structure. A parser-based test verifies one plain alternative, one HTML alternative and no additional visible body. It does not reproduce the reported email symptom, nor prove that caller-authored HTML never repeats itself. Email duplication remains unverified; do not close it based on the Slack fix.

RTS deployment verified on 2026-09-12: release ee63424-20260912144418, application revision ee634249d61c606fc0e6077486a661a0285bdf06. All three services and public health passed. The host isolation regression passed with the deployed GOG_HOME configuration.